某幅图像具有1024×768个像素点，若每个像素具有8位的颜色深度，则可以表示（请作答此空）种不同的颜色，经4:1压缩后，其图像数据需占用（ ）KBWe的存储空间。
- A.8
- B.256
- C.512
- D.1024
正确答案及解析
正确答案
解析
像素是构成数码影像的基本单元，一个像素所能表达的不同颜色数取决于每个像素的比特数（bpp）。颜色最大数可以通过取2的色彩深度次幂来得到。例如，常见的取值有：8bpp[28=256；（256色）]；16bpp[216=65536；（65,536色，称为高彩色）]；24bpp[224=16777216；（16,777,216色，称为真彩色）]；48bpp[248=281474976710656；（281,474,976,710,656色，用于很多专业的扫描仪）。像素可以用一对数字标书，例如“1024×768”，它表示横向1024像素和纵向768像素，因此其总数为1024×768像素，若采用8bpp储存，即每个像素占用1Byte，1024×768像素占用1024×768Byte的储存空间。
图像压缩是为了减少表示数字图像时需要的数据量。图像数据之所以能被压缩，就是因为数据中存在着冗余。图像数据的冗余主要表现为：图像中相邻像素间的相关性引起的空间冗余；图像序列中不同帧之间存在相关性引起时间冗余；不同彩色平面或频谱带的相关性引起的频谱冗余。数据压缩的目的就是通过去除这些数据冗余来减少表示数据所需要的比特数。由于图像数据量的庞大，在储存、传输、处理时非常困难，因此图像数据的压缩就显得非常重要。一幅1024×768像素的图像，经过4:1压缩后，占用的存储空间为1024×768÷4=196608Byte,即192KB。
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